U.S. patent number 4,189,753 [Application Number 05/913,658] was granted by the patent office on 1980-02-19 for document scanning head.
This patent grant is currently assigned to Northern Telecom Limited. Invention is credited to Robert R. Parsons, John S. S. Wei.
United States Patent |
4,189,753 |
Parsons , et al. |
February 19, 1980 |
Document scanning head
Abstract
A scanning device for use in a facsimile system is formed on a
semiconductor substrate. The substrate has an array of apertures,
the boundary of each aperture presenting a pn junction which
functions as a photodetector when appropriate bias is applied
through sensing and addressing circuits. A light is directed
through the apertures from one side of the substrate to be incident
on a document located against the other side. The boundaries of the
apertures are contoured so that the photodetectors intercept light
reflected from the document but are shielded from direct light. In
use, the document and the scanning device are slid past one another
at a rate commensurate with the rate of operation of the addressing
circuit.
Inventors: |
Parsons; Robert R. (Ottawa,
CA), Wei; John S. S. (Ottawa, CA) |
Assignee: |
Northern Telecom Limited
(Montreal, CA)
|
Family
ID: |
25433478 |
Appl.
No.: |
05/913,658 |
Filed: |
June 8, 1978 |
Current U.S.
Class: |
358/482;
348/294 |
Current CPC
Class: |
H04N
1/031 (20130101) |
Current International
Class: |
H04N
1/031 (20060101); H04N 1/03 (20060101); H04N
001/12 () |
Field of
Search: |
;358/213,285,293,294 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Britton; Howard W.
Attorney, Agent or Firm: Jelly; Sidney T.
Claims
What is claimed is:
1. A scanning device suitable for use in scanning documents, said
device comprising a substrate of semiconductor material having a
plurality of apertures therethrough, photodetector means formed in
the semiconductor material and presenting active surfaces at the
boundaries of the apertures, said semiconductor material being so
contoured at the boundaries of the apertures that the photodetector
means are substantially shielded from direct incidence of light
directed into the apertures from one side of the semiconductor
material and intercept a substantial portion of light directed into
the apertures from the other side of the semiconductor
material.
2. A scanning device as claimed in claim 1, wherein the
semiconductor material is one of the group consisting of silicon
arsenide and gallium arsenide.
3. A scanning device as claimed in claim 1, further including means
for locating a document against the outer face of the semiconductor
material at said other side thereof and means for moving the
document and the scanning device relative to one another.
4. A scanning device as claimed in claim 1, wherein the apertures
are rectangular, the photodetector means at the boundary of each
aperture comprising an element, the elements being arrayed in a
regular rectangular matrix.
5. A scanning device as claimed in claim 4, wherein the spatial
density of elements ranges from 50/sq.in., to 200/sq.in.
6. A scanning device as claimed in claim 1, wherein the
photodetector means comprises photosensitive junctions formed
between n and p type layers of the semiconductor material, and the
semiconductor material is stepped over at least a part of the
boundaries of the apertures so that one of the n and p type layers
overhangs the other layer.
7. A scanning device as claimed in claim 6, wherein electrically
conducting regions on said semiconductor material connect said
photosensitive junctions to respective sensing circuits.
8. A scanning device as claimed in claim 7, wherein electrically
conducting regions also extend between adjacent pairs of
photosensitive junctions so that the conducting state of a
plurality of photosensitive junctions can be sensed together.
9. A scanning device as claimed in claim 7, and also including an
addressing circuit to cyclically operate the sensing circuits.
10. A scanning device as claimed in claim 6, wherein at least a
part of the boundaries of the apertures taper inwardly from outer
faces of the semiconductor material to the junction between the p
and n type layers.
11. A scanning device as claimed in claim 10, wherein at least part
of the tapered boundaries follow natural crystallographic planes of
the semiconductor material.
12. A scanning device as claimed in claim 10, wherein the tapered
parts bounding the overhanging layer have an opaque coating.
13. A scanning device as claimed in claim 10, wherein an outer face
of the semiconductor material at said other side thereof has a
protective oxide layer.
14. A method of using a scanning device having a substrate of
semiconductor material, a plurality of apertures therethrough,
photodetector means formed in the semiconductor material and
presenting active surfaces at the boundaries of the apertures, the
semiconductor material being so contoured at the boundaries of the
apertures that the photodetector means are substantially shielded
from direct incidence of light directed into the apertures from one
side of the semiconductor material and intercept a substantial
portion of light directed into the apertures from the other side of
the semiconductor material, electrically conducting regions on said
semiconductor material connecting said photosensitive junctions to
respective sensing circuits to sense the condition of said
photosensitive junctions, and an addressing circuit to cyclically
address the sensing circuits, said method comprising:
locating a document to be scanned against an outer surface of the
semiconductor material at said other side thereof;
directing light through the apertures in the semiconductor material
to illuminate areas of the document; and
simultaneously with operating the addressing circuit to cyclically
address the sensing circuits;
sliding the document and the scanning device relative to one
another at a velocity commensurate with the cyclic operation of the
addressing circuit.
Description
This invention relates to a scanning device for scanning documents
and extends to a method of using such a scanning device, for
example, in connection with facsimile systems.
In scanning documents, it is often necessary to use a lens system
to produce a small image of a page being scanned. The reason is
that photodetectors usually are only obtainable in small sizes. To
make many photodetector elements, device characteristics are more
controllable if the detector array has restricted dimensions.
However, as finer optical resolution becomes necessary, a larger
number of detector elements must be accommodated on a single chip.
For example, a charge coupled device (CCD) imager may have 1728
elements on a 1" chip. Small defects in the material or in the
photomasks can easily incapacitate the entire CCD array.
The scanning device of the present invention obviates the lens
system and produces a structure in which spacing between
photodetector elements is relatively large thereby enabling reduced
tolerances in fabrication.
According to one aspect of the invention there is provided a
scanning device suitable for use in scanning documents, said device
comprising a substrate of semiconductor material having a plurality
of apertures therethrough, photodetector means formed in the
semiconductor material and presenting device surfaces at the
boundaries of the apertures, said semiconductor material being so
contoured at the boundaries but the photodetector means are
substantially shielded from direct incidence of light directed into
the apertures from one side of the semiconductor material and
intercept a substantial portion of light directed into the
apertures from the other side of the semiconductor material.
The photodetector means can comprise photosensitive junctions
between n and p type layers of semiconductor material, and the
semiconductor material can be stepped over at least a part of the
boundaries of the apertures so that one of the n and p type layers
overhangs the other layer.
The apertures are preferably rectangular, the photodetector means
at the boundary of each aperture comprising an element, the
elements being arrayed in a regular rectangular matrix.
In typical embodiments of the invention the spatial density of the
elements ranges from 50/sq.in., to 200/sq.in.
The preferred semiconductor materials are silicon or gallium
arsenide especially such materials having crystallographic
orientations permitting V-sectioned apertures to be readily etched
in the material, since, in a preferred structure, at least a part
of the boundaries of the apertures taper inwardly from an outer
face of the semiconductor material to the junction between the n
and p type layers.
The tapered parts bounding the overhanging layer should be covered
with an opaque, non-reflecting coating so that light directed into
the apertures is not reflected therefrom. The surface at the other
side of the substrate should have a protected layer of, for
example, oxide. In use a document to be scanned by the scanning
device is held against the surface at the other side of the
substrate and the document and the scanning device are slid
relative to one another so the protected layer prevents
deterioration of the p or n type layer at said other side of the
substrate.
The scanning device can include electrical conducting regions
formed in the semiconductor material for connecting the
photosensitive junctions to sensing circuits. Preferably an
addressing circuit is provided for cyclically addressing the
sensing circuits.
An embodiment of the invention will now be described by way of
example with references to the accompanying drawings, in which:
FIG. 1 is a cross-sectional view of an element of a scanning device
according to the invention;
FIG. 2 is a perspective view showing a plurality of such
elements;
FIG. 3 is a circuit diagram showing sensing circuitry and part of
addressing circuitry for cyclically sensing elements of the
scanning device; and
FIGS. 4 and 5 show bottom and top surfaces of a part of the
scanning device .
Referring to the drawings in detail, FIG. 1 shows a semiconductor
substrate 1 for example silicon, which is doped to have n-type
conductivity throughout. Afterwards, one surface of the substrate
is doped to have p-type conductivity, shown as layers 3 and 5 in
FIG. 1. With the appropriate electrical voltages applied to the n
and p sides of the substrate, a photodiode or a photosensitive
junction exists between the two layers at locations exemplified by
11 and 12. With light incident on 11, current flows between regions
4 and 5. This current is detected by a sensing circuit connected to
the regions 4 and 5.
In use, the photosensitive junctions 11 and 12 function as sensors
of a document reader. A document 13, is placed in intimate contact
with a protected layer of, for example, silicone oxide thermally
grown on the layer 5. The document is illuminated through an
aperture 7 etched in the substrate 1. By choosing a substrate with
the proper crystallographic orientation, V-shaped apertures can be
etched with excellent definition. In FIG. 1, V-shaped apertures are
fashioned on both sides of the junctions 11 and 12. The shape and
slope of the apertures are arbitrary although the V-sections is
preferred. It is important, however, that the aperture in the
region of layers 3 and 5 be wider than that in the region of layers
2 and 4. Thus the photosensitive junctions 11 and 12 are shielded
from the direct incidence of light coming from a source 8. Also,
sides 9 and 10 of the aperture are coated with an opaque film to
avoid generating reflections from the sides which may be incident
directly on the photosensitive junctions. Because of the narrow
aperture 7, only a small region of the document 13 is illuminated.
Light reflected from the document falls on junctions 11 and 12. The
size of the detected signal depends directly on the amount of light
reflected. A dark printed spot on a white document, for instance,
would reflect little light compared to that from the white
background. By moving either the document 13 or the scanning
device, it is possible to reconstruct a pattern on the document
from detected signals.
Referring to the perspective view of FIG. 2, the apertures 7 which
are in the form of windows isolate strips 14 and 15 of the p-type
layer from one another. The array of apertures 7 and the p-type
regions such as 14 and 15 are fabricated on a single substrate of
semiconductor material. A window 17 is also etched through the
protective layer 6. The strip of conducting material 18 makes
electrical contact with the p-type region 14. The conducting strip
18 is used to electrically connect together photosensors on either
side of the aperture 7 as described with reference to FIG. 5.
Conducting strips similar to 18 are used also on the substrate for
connection to the sensing and addressing circuitry.
In order to detect the light induced signals, a column and a row
electrical addressing circuit is used as shown in FIG. 3. A p-type
region, such as 14 in FIG. 2, together with the associated
photosensitive junction 11, is symbolized as 20 in the FIG. 3.
Region 19 and its photosensitive junction are shown as 20a in FIG.
3. In an electrical addressing scheme used, 20 and 20a are labelled
(1,1) and (1,2) respectively. The column label is the first number
in the bracket and the row label the second. When a column 1
terminal, 25, is pulsed to a positive voltage, for example 5 volts,
devices 20 and 20a are properly biased to collect current generated
by incident light. The current from (1,1) is AC coupled through a
capacitor 27 to an amplifier 29 and resistor 28, resulting in an
output signal at a terminal 30. The light induced signal from
(1,2), on the other hand, appears at terminal 34, after similar
amplification. When terminal 25 is pulsed positive, terminals 26,
35, 36, etc. are held at zero voltage by a timing circuit (not
shown). Thus only the photosensitivities of elements (1,1) and
(1,2) are enhanced. Thus signals from a particular column are
identified by pulsing only that column positive while holding all
the rest at zero voltage. Interconnecting lines such as 23 and 24
are fabricated on the substrate. Therefore, instead of lines
addressing the elements individually, a considerably small number
of external connections suffices. In practice, each column has more
than two elements shown in FIG. 3. For example, 1600 photosensitive
elements can be connected in a 40 column by 40 row matrix. Only 80
external connections need be made, 40 for column terminals such as
25 in FIG. 3, and 40 for outputs such as 30 in FIG. 3. In the
circuit of FIG. 3, lines 23 and 24 are held at AC ground by action
of the amplifier 29. Because of the photosensor characteristics of
elements such as 20, little current can flow when the column
terminal, for example, 25 is held at ground. Capacitor 27 is used
to block leakage current through the photosensitive junctions in
the absence of light; with low leakage, the capacitor can be
dispensed with.
An exemplary pattern of electrical connections to the
photosensitive sides 11 and 12 is shown in detail in FIGS. 4 and 5.
The substrate 1 is heavily doped n type so that regions such as 2
and 4 shown in FIG. 1 as the bottom of the substrate are
sufficiently conducting. Detectors 14 and 19 shown in the top
elevation of FIG. 5 can be connected in parallel by a block contact
37 at the bottom of the substrate as shown in FIG. 4. The contact
37 corresponds to the column terminal 25 in FIG. 3. If the
substrate is thick compared to the spacing between photosensors, a
voltage applied to 37 may affect other photosensors in parallel
with 14 and 19. A zig-zag type of detector arrangement can be used
to solve this problem. Thus as shown in FIG. 4, the second column
connection 38 is made on the side opposite to 37, across the line
of apertures 39. The connection 38 would correspond to column
terminal 26 in FIG. 3. In effect, only half the available
photosensors are in use. The two sensors between (1,2) and (3,1),
for example, are not used. This redundancy alleviates problems in
manufacturing yield; only half the photosensors have to function.
The row connections are shown in FIG. 5. Element (1,1) is connected
to element (2,1) by a conducting strip 18 shown in part in FIG. 1.
A similar strip connects (1,2), (2,2) and (3,2).
In a typical embodiment of the invention the spatial density of
apertures is of the order of 200/sq.in., the area of the apertures
is of the order of 25 sq.mm. and the area of the photosensitive
junctions at each aperture is also of the order of 25 sq.mm.
* * * * *